The present invention relates to an air-conditioning system, in particular for the air conditioning of an airplane cabin, comprising at least two air-conditioning plants which are in communication in each case on the inlet side with a supply line and on the outlet side with a cabin to be air conditioned or with a mixing chamber, with the supply line on the inlet side having at least one flow regulating valve in each case for the purpose of regulating the flow.
An air-conditioning system of the aforesaid type is used for the heating/cooling of the cabin, for the supply of fresh air to the passengers and crew and for the optimum pressurizing of the cabin.
To be able to fulfill the aforesaid functions not only in normal operation, but also in the case of malfunction, i.e. with a partial failure of the plant, air-conditioning systems with a redundant design are known. The construction size and the weight must in particular be kept as low as possible on use as an airplane air-conditioning system.
To fulfill these functions, the following two embodiments of an airplane air-conditioning plant are known:                a) an air-conditioning system comprising at least two separately arranged plants and without internal redundancy. The redundancy is hereby achieved by the second plant.        b) an air-conditioning system comprising at least one plant and internal redundancy. The redundancy is achieved in this case by the components partly present in duplicate.        
FIG. 1 shows an air-conditioning system in accordance with variant a). At least two usually identical air-conditioning plants are used here to satisfy the required functions. It is ensured that even if one plant fails in total, the second plant still fulfils the minimum requirements. As can be seen from FIG. 1, each of the air-conditioning plants is charged with supply air on the inlet side. The corresponding supply line is in each case provided with a flow regulating valve by means of which the respective flow on the pressurized air side can be regulated by the air-conditioning plant. On the outlet side, the air-conditioning plants are in communication with a mixing chamber into which furthermore circulating cabin air is introduced and which is in communication on the outlet side with the cabin and which supplies the latter with the correspondingly conditioned air. On the outlet side, the air-conditioning plants furthermore have check valves as can be seen from FIG. 1.
The function of such an air-conditioning plant can be seen from FIG. 2. Each of the air-conditioning plants (air-conditioning plant 1, air-conditioning plant 2) has a flow regulating valve FCV upstream of it. This valve serves for the regulation of the pressurized air passage of the respective air-conditioning plant and contains a flow measuring device and a pneumatically/electrically actuated valve for continuous flow regulation. If one of the air-conditioning plants should be switched off, the associated flow regulating valve FCV is completely closed.
Hot pressurized air from the engines or from an auxiliary unit is supplied to the flow regulating valve FCV. This has a temperature of approximately 200° C. and a pressure of approximately 3 bar. This air is pre-cooled to approximately 100° C. in the first heat exchanger on the pressurized air side (pre-heat exchanger or primary heat exchanger PHX) and subsequently further compressed in a compressor C. The pressurized air then flows for further cooling into the second heat exchanger on the pressurized air side (main heat exchanger or secondary heat exchanger (SHX) and is cooled here to approximately 40° C. The dehumidification subsequently takes place in a water extraction system. This consists of the components reheater REH, condenser CON and water extractor WE.
The air dehumidified in this manner is expanded in the turbine T and cooled in this process to approximately −30° C. The shaft power arising at the turbine in this process is used to drive the compressor C and a fan FAN which is arranged in the stagnation air duct and serves for the conveying of PHX/SHX stagnation air or ambient air. The air then flows from the turbine outlet through the cold side of the condenser CON and subsequently into the mixing chamber or into the cabin.
The said procedure takes place in normal operation in the air-conditioning plant 1 and in the air-conditioning plant 2 in accordance with FIG. 2.
For the purpose of regulating the temperature or the cooling capacity of the plant, a valve TCV is provided in each case which permits a variable bypass of the compressor C, main heat exchanger SHX and turbine T. Furthermore, the stagnation air volume can be varied by means of valves at the stagnation air duct inlet and/or outlet (RAIA and RAOA).
In addition to the fan FAN, the fan bypass with a check valve GCKV 1 is also located in the stagnation air duct, whereby the transmission of the stagnation air duct is increased in flight.
If a shaft device ACM consisting in the present case of a fan FAN, a compressor C and a turbine T fails, the train of this partially defective plant can still be used for pressurized air transport in air, however with reduced cooling capacity, whereby the second still intact plant is supported with respect to flow and cooling capacity. The cooling of the pressurized air in the partially defective plant takes place in this process only by the stagnation air heat exchanger PHX, SHX, without an expansion being able to take place in the failed turbine T.
A complete failure of an air-conditioning plant occurs when, for example, a line breaks, for example the line from the flow regulating valve FCV to the pre-heat exchanger PHX, or when a flow regulating valve FCV closes incorrectly. In this case, the pressurized air supply of the corresponding air-conditioning plant is lost, whereby it fails completely. To meet the required minimum airflow, the remaining plant must convey approximately 30% more flow.
It results from this that the largest performance losses in flight for the air-conditioning system in accordance with FIG. 2 thus occur when a flow regulating valve closes incorrectly or if a line break occurs. Both actions are linked to the failure of one of the air-conditioning plants. In contrast, the failure of a shaft device only means a power reduction of the respective air-conditioning plant since PHX and SHX of this plant are still available for the cooling.
Due to the relatively complex design of the flow regulating valve FCV, a defective closing of this valve is much more probable than a line break or a heat exchanger break. A clear power reduction of the air-conditioning system in flight thus primarily results due to an incorrect closing of the flow regulating valve FCV. The reasons for this can be the failure of the valve mechanism, the failure of the valve actuation or the failure of the flow measurement of the flow regulating valve.
In addition to the architecture described by way of example and shown in FIG. 2 with a 3-wheel ACM per air-conditioning plant, other plant concepts are naturally also possible such as a 4-wheel ACM per plant or two serially arranged ACMs per plant or also motorized ACMs. Furthermore, different dehumidification systems are feasible.
The embodiment of the shaft device and of the dehumidification system does not, however, change anything in the general circumstances that at least two separately arranged air-conditioning system are used to fulfill the redundancy demands.
In addition to air-conditioning system with two separately arranged air-conditioning plants, air-conditioning systems in accordance with variant b) are likewise known which have a plant with internal redundancy. The redundancy is achieved in that components of the plant are partly present in duplicate.
Components with a relatively high failure possibility and significantly negative system effects such as the shaft device ACM and the flow regulating valve FCV are present in duplicate in this system. An air-conditioning system with partially multiply present components is known from EP 0 891 279 B1.
FIG. 3 shows an air-conditioning system with a shaft device ACM1, ACM2 present in duplicate and with a flow regulating valve FCV1, FCV2 provided in duplicate.
The stagnation air heat exchangers PHX, SHX and the water extraction system consisting of the components REH, CON, WE are, in contrast, only present once.
A relatively compact construction thereby results and thus low construction space requirements compared to the system architecture shown in FIG. 2.
The basic cooling process itself is identical to the process described with reference to FIG. 2.
In normal operation, the flow regulating valves FCV1, FCV2 provided in duplicate for reasons of redundancy are supplied with hot pressurized air (approximately 200° C. and 3 bar) from the engines or from an auxiliary unit. These valves include a flow measurement device and a pneumatic/electrical valve for the continuous flow regulation. If the air-conditioning system should be switched off, both valves FCV1, FCV2 are fully closed.
The FCV outlet air is merged and pre-cooled to approximately 100° C. in the joint stagnation air heat exchanger PHX. Approximately half of the PHX outlet air in each case is compressed in the compressor C1 and in the compressor C2 and is cooled to approximately 40° C. by the stagnation air after the merging in a secondary heat exchanger SHX. For condensation and water separation, the cooled pressurized air is guided through the reheater REH, the condenser CON and the water extractor WE. The pressurized air is subsequently divided again and in each case approximately half is expanded in turbine T1 and in turbine T2 and cooled in this process to approximately −30° C. After merging, this air flows through the cold side of the condenser CON and finally by means of a joint line into the mixing chamber of the airplane.
In the architecture shown by way of example in FIG. 3, each shaft device ACM1, ACM2 consists of three wheels which are connected by a shaft. The turbine shaft performance is used for the driving of the compressor C1, C2 and of the fan FAN1, FAN2. The fans FAN1, FAN2 are arranged in parallel so that each fan transports approximately half the stagnation air through the joint PHX and SHX on the ground. In flight, the flow from the PHX and SHX with stagnation air takes place here mainly due to the stagnation pressure.
The stagnation air is supplied to the main heat exchanger SHX and to the downstream per-heat exchanger PHX on the stagnation air side in a duct and is sucked through a common duct by the two fans FAN1, FAN2 after the PHX. This stagnation air then flows back to the environment via two separate fan outlet ducts.
The temperature regulation of the cooling air as a rule takes place by means of two valves TCV1, TCV2 and of the stagnation air duct valves RAIA, RAOA1 and RAOA2. The valves TCV1 and TCV2 additionally serve to ensure a synchronous operation of the two shaft devices.
A typical error case in the architecture of the air-conditioning system shown in FIG. 3 is the failure of a shaft device ACM. In this case, certain minimum requirements with respect to air volume and cooling capacity must be also be ensured. In order also to satisfy these functions in the error case, two additional valves SOV1, SOV2 are arranged at the respective turbine inlet as can be seen from FIG. 3. Furthermore, two additional check valves CCKV1, CCKV2 are integrated at the respective compressor inlet of the compressors C1, C2.
If e.g. the shaft device ACM1 fails (seized shaft), the check valve CCKV1 prevents a useless circular flow of the air compressed by the compressor C2 in operation via the compressor C1 back to the inlet of the compressor C2. The valve SOV1 is closed so that the air compressed by the compressor C2 is not expanded uselessly via the standing turbine T1, but only via the functioning turbine T2 of the ACM2 in operation.
Due to the failure of an ACM, the remaining intact ACM should now convey the total air. This is, however, not possible since each ACM is designed for weight and construction size reasons only for approximately 50% of the total air volume (normal operation) and cannot cope with double the air volume. To achieve the necessary transmission, a partial bypass of the remaining functioning ACM2 is thus required by opening the valve TCV2 or by an over-dimensioned plant (with respect to normal operation)
In ground operation (no stagnation pressure) and if the shaft device (e.g. ACM1) has failed, the associated stagnation air duct outlet valve RAOA1 must be closed, since otherwise the functioning fan FAN2 would suck in the air from the oppositely disposed outlet duct and not through the stagnation air heat exchangers PHX, SHX. This system architecture therefore requires at least two controllable stagnation air outlet valves as is reproduced in FIG. 3.
In addition to this architecture described by way of example with two 3-wheel ACMs per plant or per jointly used heat exchanger, other plant concepts are naturally also possible such as two 4-wheel ACMs arranged in parallel per plant or at least two serially arranged ACMs per plant or motorized ACMs or also different dehumidification systems. The design and arrangement of the ACMS can be as desired, i.e. apart from the exemplary said 3-wheel and 4-wheel machines and their arrangements, any other variants are feasible.
The embodiment of the shaft device and of the dehumidification system does not, however, change anything in the general circumstances that at least two separately arranged air-conditioning system are used to fulfill the redundancy demands.
The embodiments described above of an air-conditioning system in accordance with FIG. 1, FIG. 2 or FIG. 3 are associated with the disadvantages listed in the following:    1. Two identical and separately arranged plants in accordance with FIG. 1, FIG. 2:            The failure of a flow regulating valve FCV results in the failure of an air-conditioning plant. To also achieve the required cooling capacity and the required air flow in this error case, the plant must be designed for this case. This means that under normal conditions, when both plants are in operation, the air-conditioning system is over-dimensioned. The designing for this error case (only one plant functional) requires larger heat exchangers PHX/SHX and a larger stagnation air duct and line cross-sections. This is associated with corresponding disadvantages with respect to the construction size and weight of the air-conditioning plant.        Whereas the failure of the supply air due to a failure of a flow regulating valve can be largely avoided by the installation of two flow regulating valves and flow measuring devices arranged in parallel per air-conditioning plant, since the probability of the failure of the supply air due to an incorrect closing of both flow regulating valves is very low. Such a system results from FIG. 4. However, at the same time, the probability that at least one flow regulating valve is incorrectly open doubles. This can result in a very high, uncontrolled flow and thus to extreme pressure and temperature demands in the air-conditioning plant. These high strength demands can likewise result in the switching off of the corresponding plant to avoid damage by overload (e.g. line break).        The use of two flow regulating valves per plant is furthermore disadvantageous because the costs and the weight of the air-conditioning system thereby increase considerably, while the system reliability is reduced, which is due to a higher number of components.            2. A plant present once with components partly available in duplicate in accordance with FIG. 3.            In comparison with the embodiment in accordance with FIG. 1, FIG. 2, two valves SOV1 and SOV2 and two check valves CCKV1, CCKV2 are required as additional components.        Furthermore, the guaranteeing of synchronous operation of the two shaft devices ACM1, ACM2 requires an additional monitoring and regulating effort. On the failure of a shaft device, a fast actuation of the valves (e.g. SOV) is necessary to ensure correct operation and the satisfaction of the functions, pressurizing, venting and cooling. Another disadvantage results in that specific components are only present once such as the line from the FCV1 and FCV2 to the PHX, heat exchanger, line from the air-conditioning system to the mixing chamber. A failure of only one of these components, for example a line break, results in the total failure of the total air-conditioning system. In contrast to this, with two or more separately arranged air-conditioning plants, a line break results, for example, only in the failure of one of the air-conditioning plants, that is e.g. in the failure of one of two air-conditioning plants.        If a shaft device fails, the cooling capacity and transmission of the system is much lower in comparison to the embodiment in accordance with FIG. 2.        If e.g. the ACM 1 in accordance with FIG. 3 fails (fixed shaft), the check valve CCKV1 prevents the compressed air from the compressor C2 in operation from flowing back via the compressor C1 to the inlet of the compressor C2 (useless circular flow). As explained above, the valve SOV1 is closed so that the air compressed by the compressor C2 is not expanded uselessly via the standing turbine T1, but only via the functioning turbine T2. Due to the failure of an ACM, the remaining intact ACM should now convey the total air. As explained above, this is, however, not possible since each ACM and the corresponding line cross-sections are only designed for approximately 50% of the total air volume (normal operation) and cannot cope with double the air volume. The transmission and the cooling capacity of the plant is thereby greatly reduced in the defect case because an at least partial bypassing of the ACM and of the main heat exchanger SHX is necessary (TCV still open).        This disadvantage can also only be insufficiently compensated by an overdimensioning of the ACMs, i.e. the design takes place e.g. to 70%, instead of 50% of the total flow, because the construction space requirements and the weight and the costs of the ACMs thereby increase. It must be taken into account in this process that the weight of a component substantially represents a function of the flow.        
Whereas in an embodiment with two separately arranged air-conditioning plants, a failure of the flow regulating valve results in a significant reduction in performance of the air-conditioning system, in an embodiment with one plant and components partly present in duplicate, the failure of the shaft device or of the additional valves SOV1 and SOV2 results in considerable losses in performance.